Large-scale dynamical phenomena during solar activity cycles
Francesco Feminella and
Received 10 July 1996 / Accepted 18 November 1996
The long-term behaviour of several solar-activity parameters (spots, flares, radio and X-ray fluxes) was investigated to identify essential characteristics of the 11-year cycle maximum. We confirm past findings suggesting that activity maxima occur at least twice during a cycle: first, near the end of the rising activity phase and then in the early years of the declining phase. However, we show that the double peak is more distinct when intense and/or long-lasting events are considered, because low-energy and short-duration events tend to follow a single-peaked 11-year cycle. Moreover, structured activity maxima are detected in all the solar atmospheric layers (photosphere, chromosphere and corona) up to interplanetary space, where several indices display a clear trace of the dual-peak maximum. Results based on some activity indices for cycle 21 support the effectiveness of the heliomagnetic cycle in producing the structured shape of the maximum phase of solar activity cycles.
Key words: Sun: activity; sunspots; radio radiation; flares; X-rays; magnetic fields
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© European Southern Observatory (ESO) 1997
Online publication: June 30, 1998